Dissipative bracing-based seismic retrofit hypothesis of an elevated water storage tank with R/C frame staging structure

A seismic performance assessment and supplemental damping-based retrofit study on a heritage reinforced concrete (R/C) elevated water storage tank is presented. The structure was built in the early 1930s as water supplier for the coal power plant of Santa Maria Novella Station in Florence, and is still in service. The tank has a R/C frame supporting structure and is currently used as water supplier for trains and platform services. The dynamic behavior of the fluid is simulated by a classical convective plus impulsive mass model, for which a discrete three-dimensional schematization is originally implemented in the finite element analysis. The time-history assessment enquiry highlights a remarkable plastic response of the frame structure under seismic action scaled at the maximum considered earthquake level. Based on these results, a retrofit hypothesis is proposed, consisting in the installation in the staging structure of a dissipative bracing (DB) system incorporating pressurized fluid viscous spring-dampers. The DB technology, studied by the first two authors during the last two decades by focusing on the numerical and analytical modeling, the experimental characterization and verification, the definition of design procedures, and the development of several applications to R/C and steel frame building structures, is explored for the first time within the study reported here for the seismic retrofit of elevated tanks. The mechanical parameters, design criteria and technical implementation details of the rehabilitation strategy are illustrated. The verification time-history analyses in protected conditions show that a substantial enhancement of the seismic response capacities of the structure is attained as compared to its original configuration, with little architectural intrusion, quick installation works and low costs.